News - April 19, 2001


 NSF PR 01-33
 Media contacts:
              Cheryl Dybas, NSF
                                   (703) 292-8070
                                              cdybas@nsf.gov

              Anatta, NCAR
                                   (303) 497-8604
                                              anatta@ucar.edu

              Stephanie Kenitzer, American
              Meteorological Society
                                   (425) 432-2192
                                              kenitzer@dc.ametsoc.org
 Program contact:
              Jay Fein, NSF
                                   (703) 292-8527
                                              jfein@nsf.gov




 Scientists Suggest New Index to Capture "Flavors" of El Niņo

 Just as the Federal Reserve uses more than one index to measure the health and state of the economy,
 scientists at the National Center for Atmospheric Research (NCAR) believe it is essential to have at
 least two climate measures to capture all "flavors" of El Niņo.

 Climate scientists have long used changes in sea surface temperatures in specific regions of the Pacific
 Ocean to characterize El Niņo events. But using just that one temperature index does not give a
 complete picture of the climate phenomenon, according to scientist Kevin Trenberth of NCAR.

 "El Niņo comes in many different flavors, "said Trenberth. "Each has a different and distinct character.
 An index of average sea surface temperature variations in some parts of the Pacific Ocean does not
 allow us to differentiate between major, moderate and minor El Niņos, or between the entire nature of
 the event and its evolution."

 Writing in the April 15 issue of the American Meteorological Society's Journal of Climate, Trenberth
 and colleague David Stepaniak, propose a second El Niņo index called the "Trans-Niņo Index" or TNI.
 This new mathematical equation calculates the difference between sea surface temperature changes in
 the central equatorial Pacific Ocean and those in waters along the coast of South America. Showing
 different developments across the Pacific allows scientists to see how and where El Niņo events have
 developed over the last 50 years and to detect changes that may be occurring on a decadal time scale.

 In his research Trenberth found that although El Niņo events tend to be locked to the annual cycle and
 typically peak in the northern winter, the evolution of El Niņo has changed substantially. The TNI
 shows that El Niņo events between 1950 and 1976 tended to develop first along the coast of South
 America and then spread westward. More recent El Niņo events developed in the central Pacific and
 spread eastward.

 "Trenberth's and Stepaniak's study, which has resulted in an innovative way of differentiating between
 El Niņos of various strengths and characters, should lead to a better understanding of the dynamics of
 El Niņos--and their improved prediction," said Jay Fein, director of the National Science Foundation
 (NSF)'s climate dynamics program, which funded the research.

 "We want to explore whether we can use the relationships of temperature variations between the
 different parts of the Pacific to evaluate numerical climate models on how well they simulate El Niņo
 events," added Trenberth. "Our goal is to capture that character so we can improve confidence in
 future predictions."

                                   -NSF-